It is well known that certain body organs, notably the heart, bladder, phrenic nerve, and carotid sinus are susceptible to artificial stimulation and sensing, employed when their natural functioning becomes impaired in some manner. Artificial stimulation is normally accomplished by the implantation into the body of the patient of an electrical pulse generator which is connected to the tissue of the failing organ through an electrically conductive lead assembly. The distal end of this lead assembly is placed into contact with the tissue of the organ, while the proximal end is placed into contact with the output terminals of the pulse generator. A well known example, discussed herein by way of example and not of limitation, of this medical technique concerns stimulation of the human heart.
Heart stimulators and lead assemblies are well known, and have been of two general types: unipolar or bipolar. In a unipolar device, the stimulator has a single output terminal, and the metallic case of the device serves as the complementary electrode. Thus, the stimulating impulse can be supplied to the heart or other tissue via a single conductor lead, and the circuit is completed through body tissue and fluids. In a bipolar device, the stimulator has two output terminals, and the case plays no part in the circuit. This type stimulator utilizes a two conductor lead, each conductor terminating in a distal electrode. Such a two conductor lead may also find application with unipolar devices having a sensing input. In this situation, one conductor would handle impulse transmission to the heart or other tissue, while the other conductor relays information about the selected tissue back to the stimulator.
After implanting such a device and its lead assembly into the body of a patient, the physician will check the minimum effective impulse level, or threshold, of the distal electrodes to verify electrical contact with the heart, or other tissue, to assure proper stimulator and sensing thresholds. At this time, in the case of a two conductor lead assembly, the physician may discover that a better stimulating threshold exists at the complementary electrode of a bipolar stimulator, or at the sensing electrode of a unipolar stimulator. If this occurred, the physician would want to change the function of these electrodes so that stimulating pulses could be accomplished through the electrode having the most advantageous threshold condition.
Another situation that may develop occurs when, over a period of time, fibrotic (and scar tissue caused by the contact between the distal electrodes and the heart) growth alters the threshold characteristics at the primary stimulating electrode. Again, to improve this situation, the physician might want to stimulate through the secondary electrode.
To correct either of these situations, the physician could reposition the primary electrode in the hope of locating a position with a more favorable threshold. At the time of implantation, this relocation would be possible, but extremely difficult. However, to attempt a relocation after fibrotic growth has overtaken the electrodes could very possibly result in traumatic injury to heart tissue and venous connecting paths.
Most prior art lead and stimulator assemblies have been designed to function in only one configuration.
Where provision has been made for altering an electrode function, the resulting female connector assembly design has remained bulky at a time when implanted assemblies and leads were being reduced in size to facilitate implantation. These same conditions and problems exist with body implantable tissue stimulators utilized with the other body organs susceptible to artificial stimulation.
To overcome the disadvantages of prior art tissue stimulators and lead assemblies, apparatus and methods are provided to allow a physician to conveniently alter the function of a lead assembly, either at the time of implantation, or later, if the heart's reaction to the presence of the distal electrodes indicates that a change would be advantageous.
Accordingly, it is a feature of the invention to provide a reduced volume female connector and electrode assembly which permits alteration of the function of the distal electrodes of the lead assembly.
It is a further feature of the invention to accomplish this alteration of function by only axial relocation of the proximal connector assembly.
One other feature is a reversible function electrode assembly having coaxial proximal connectors spaced axially apart.
It is an object of the present invention to provide for altering the stimulus from an electrode without physical relocation of an implanted distal electrode.
Another object is to provide a variable function female connector assembly with a space envelope of a single function female connector assembly.
.Iadd.Another object of the invention is to provide a method for reversing the function of an electrode assembly of a tissue stimulator.
A further object of the invention is to provide a method and apparatus for conductively connecting a multiple function lead assembly with a female connector assembly of a tissue stimulation device to permit alteration of the function of distal tissue stimulation electrodes of the lead assembly. .Iaddend.